Eastern Kentucky University

Poster Title

Changes In Water Use Efficiency and Xylem Production of Two Pinus Strobus Plantations

Institution

Eastern Kentucky University

Abstract

Pinus strobus (eastern white pine) is a valuable timber species common throughout eastern North American forests. Understanding the relationship between climate and water use efficiency (WUE) and annual aboveground biomass production (ANPP) in this species will help us understand how it may respond to future climatic conditions. Randomly stratified permanent plots were established in the Coweeta basin in north- and south-facing watersheds planted with P. strobus ca. 50 years ago. From each plot, we randomly-selected two trees and extracted one increment core from each tree. Annual growth was measured on each core and regressed against climate data to determine climatic sensitivity. Cores were then separated into annual rings, which were digested to α-cellulose for stable carbon isotope analysis (13C). ANPP was estimated using reconstructed annual tree diameters and allometric equations. We found that trees on the north-facing watershed were more productive compared to trees in the south-facing watershed during the first 30 years. After this time, however, the difference between the two watersheds began decreasing, and in the early 1990s, trees in the south-facing watershed became more productive. This change in radial growth trend coincided with a change in estimated watershed evapotranspiration. The south-facing watershed appears to be using water more conservatively while out-producing the north-facing watershed, indicating that WUE has been increasing over time. These results could imply that trees in the south-facing watershed have acclimated to the higher levels of water stress and are able to maintain productivity without requiring as much water. If evaporative demand continues to increase as a result of climate change, the south-facing watershed might continue to out produce the north-facing water.

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Changes In Water Use Efficiency and Xylem Production of Two Pinus Strobus Plantations

Pinus strobus (eastern white pine) is a valuable timber species common throughout eastern North American forests. Understanding the relationship between climate and water use efficiency (WUE) and annual aboveground biomass production (ANPP) in this species will help us understand how it may respond to future climatic conditions. Randomly stratified permanent plots were established in the Coweeta basin in north- and south-facing watersheds planted with P. strobus ca. 50 years ago. From each plot, we randomly-selected two trees and extracted one increment core from each tree. Annual growth was measured on each core and regressed against climate data to determine climatic sensitivity. Cores were then separated into annual rings, which were digested to α-cellulose for stable carbon isotope analysis (13C). ANPP was estimated using reconstructed annual tree diameters and allometric equations. We found that trees on the north-facing watershed were more productive compared to trees in the south-facing watershed during the first 30 years. After this time, however, the difference between the two watersheds began decreasing, and in the early 1990s, trees in the south-facing watershed became more productive. This change in radial growth trend coincided with a change in estimated watershed evapotranspiration. The south-facing watershed appears to be using water more conservatively while out-producing the north-facing watershed, indicating that WUE has been increasing over time. These results could imply that trees in the south-facing watershed have acclimated to the higher levels of water stress and are able to maintain productivity without requiring as much water. If evaporative demand continues to increase as a result of climate change, the south-facing watershed might continue to out produce the north-facing water.